The Universal Serial Bus (USB) standard was initially offered as a truly easy-to-use universal interface for the PC. Since then, USB has gained widespread acceptance. From the user perspective, the benefits of USB include universal plug-and-play and relative ease-of-use. When a USB peripheral is plugged-in to a USB port on a PC, the system will auto-detect and auto-configure the device. In most cases, there is no user intervention required. This is a significant improvement over the prior technology when a user had to open the PC to install a component. The USB interface also eliminates the need for multiple I/O standards, thereby simplifying PC connectivity for the consumer (as well as simplifying manufacturing for the PC Original Equipment Manufacturers (OEMs).
A USB cable is used to connect a peripheral device with a host device, such as a PC, to enable communication between the devices. A typical USB cable includes a positive voltage (Vcc) line, a ground line, a positive data line, a negative data line, and a cable screen. The Vcc line nominally carries 5 volts and can be used by a host to supply power to a peripheral device. The positive and negative data pins are used to transmit data using differential signaling.
The cable screen is connected to the “shell” of the connector at the host end of the cable. Typically, the corresponding receptacle “shell” is connected to the electrical ground within the host device, but not connected directly to ground inside the peripheral device. In many cases, the screen is connected to ground inside the peripheral via a large resistor and a small capacitor, as this has been found to provide the best compromise between electro-static discharge (ESD) and radio frequency interference (RFI) suppression.